/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.commons.udf.service;

import org.apache.iotdb.commons.file.SystemFileFactory;

import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.concurrent.atomic.AtomicLong;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class UDFClassLoader extends URLClassLoader {

    private final String libRoot;

    /**
     * If activeQueriesCount is equals to 0, it means that there is no query using this classloader.
     * This classloader can only be closed when activeQueriesCount is equals to 0.
     */
    private final AtomicLong activeQueriesCount;

    /**
     * If this classloader is marked as deprecated, then this classloader can be closed after all
     * queries that use this classloader are completed.
     */
    private volatile boolean deprecated;

    public UDFClassLoader(String libRoot) throws IOException {
        super(new URL[0]);
        this.libRoot = libRoot;
        activeQueriesCount = new AtomicLong(0);
        deprecated = false;
        addURLs();
    }

    private void addURLs() throws IOException {
        try (Stream<Path> pathStream =
                     Files.walk(SystemFileFactory.INSTANCE.getFile(libRoot).toPath())) {
            // skip directory
            for (Path path :
                    pathStream.filter(path -> !path.toFile().isDirectory()).collect(Collectors.toList())) {
                super.addURL(path.toUri().toURL());
            }
        }
    }

    public void acquire() {
        activeQueriesCount.incrementAndGet();
    }

    public void release() throws IOException {
        activeQueriesCount.decrementAndGet();
        closeIfPossible();
    }

    public void markAsDeprecated() throws IOException {
        deprecated = true;
        closeIfPossible();
    }

    public void closeIfPossible() throws IOException {
        if (deprecated && activeQueriesCount.get() == 0) {
            close();
        }
    }
}
